Apparatus for cracking hydrocarbon oils



Patented Jan. 18, 1944 Aaron B. Bags'ar, Drcxel Hill, Pa., assignor to Sun Oil company, Philadelphia, Pa., a corporation or New Jersey at Drawing... Application August 5, 1942,

' Serial No. 453,713

2 claims. (or. 196-133) footed by a purely thermal process in tubular eon Stills and is also efiecte'd catalytically, at lower, butv still high, temperatures, in catalytic case tubes. As is well known, when such stills are compose of. ordinary carbon steel, the sulfur 'c'ont'aiiied in the oil is converted to Hydrogen sulfide and other Sulfur compounds, which all-- ack 511d corrode the steel and materially shorten the life of the still. I Iti's known, however, that resistance to corrosion may be. 'm'aterially increas by making the stills, or, the tubular elemerits thereof, of a low carbon alloy "steel containing, in addition to a percenta e of manganese within the usual range of carbon steel, a per heritage of chromium not less than 4%, to which usually added about .'5% of molybdenum. A typical commercial composition is: (3.12%, Mn 31%, Cr 4.6% and Mo .50%.

Ihave discovered that the reliability and efcien'cy of stills for decomposing hydrocarbon oils at high temperature made of alloy steel of a composition similar to that specified is materially lessened when, as is usually or frequently the case, an appreciable percentage of salt is present in the oil, since chromium steels are more liable than carbon steel to corrosion by chlorides. I have also discovered that, in commercial chromium steels of the order of that above specified, it is possible to largely replace the chromium by nickel and thereby materially decrease the corrosion due to the presence of salt without diminishing resistance to corrosion due to sulfur. I have also discovered that resistance to corrosion is still further increased by utilizing a percentage of silicon greater than that usually present in carbon steel, the silicon securing increased resistance to sulfur and salt corrosion on the inner surface of the tubes e posed to sulfur-containin hydrocarbons and increased resistance to sulfur corrosion and oxidation on the outer surface of the tube produced by combustion products of the fuel. Molybdenum is known to increase the strength of the alloy at high temperature and for reducing susceptibility to embrittlement. It is also possible to replace the silicon in part with aluminum, which performs essentially the same function as silicon except that it does not substantially reduce salt corrosion, and which I have found, even when added in a much smaller percentage than one per cent, reduces scaling and oxidation of the steel to a far greater extent than silicon alone. In some service conditions, however, aluminum-bearing chromium steel, even when containing molybdenum, is susceptible to embrittlement and it is therefore desirable to add a substantially smaller percentage of aluminum, preferably less than 1%, than wouldbe desirable if resistance to oxidation were the only factor to be considered; in other words, to add aluminum, if added at all, only when molybdenum is added in sufiicieni; proportion to counteract the embrittling tendency of the aluminum. It is also desirable, but not necessary, to add titanium, which, besides increasing the tendency to scaling, reduces the air-hardening tendency of the steel especially if the steel contains over one per cent. of chromium; It is also desirable, but notneces:

sary, to add vanadium, and thereby obtain other tion and structural uniformity. i I

The following composition is found to be rneas urably superior in corrosion resistance to the commercial chromium-molybdenum steel herein:- before mentioned:

0 .14%,Mn .44%, or .s%, I Ni 1.5%, Si 1.2%, M0 5% It will be observed that in this composition the percentage of each of the elements Ni and Si is substantially higher than the percentage of desirable properties, including carbide stabilizaf Cr; that the percentage of Si is not much lower than that of the Ni, and that the combined pen centage of alloying elements, other than C and Mn, is only 4 The following are other example compositions that are highly resistant to corrosion:

11 III 1V7 V VI VII In general, the smaller the percentage of carbon the better. A carbon percentage of .25 is about the permissive maximum. Its percentage should not exceed about .2 and is preferably considerably lower. A carbon percentage as low as .06% is commercially practicable. The only objection to steel containing very little or no carbon is theexpense of its production.

The permissive ranges of alloying elements other than carbon are:

Cr less than 2%, preferably not over 1.5% and desirably a fraction of 1%, and below the percentage of nickel and below th percentage of silicon if aluminum is not added and below the percentage of silicon and aluminum if. both be added, and preferably below the percentage of silicon even if aluminum be added.

Manganese .2 to 1%.

Silicon .6 to 2.5%, but preferably f. 1 T10.- between .6 .or r

31% and 1.5 or 1.6%, and preferably above the percentage of chromium, and alway together with aluminum, if aluminum beadded; abovethe H percentage of chromium. The percentage of silicon, or of silicon and aluminum if the latter be added, should not be less than half, and may ex-- v ceed, the percentage of nickel.

- i ,g, u w H temperature required to effect their decomposition or conversion.

In claiming iron approximately su-fiicient to complete the 100%, I do not mean to exclude the addition of elements not specified in the claims but described in the specification as desirable addition in .the smallproportion ranges stated, nor to exclude the addition of very small proportions of other elements whose addition would not iunfavorably afiect the function of the elements particularly recited.

application filed by me August 28, 1940, Serial What I claim and desire to protect by Letters Patentisz 1 1. Aistill for use in a process wherein hydrocarbon oils'containing impurities including both and oxidation when the oil contains an appre- V ciable percentage of salts, although deviations therefrom within the wider ranges specified give a substantially higher resistance to corrosion and oxidation than in steel containing relatively high percentages of chromium and relatively low percentages of silicon, even when. nickel is added in .considerable proportion to largely replace the chromium. While, the entire elimination of chromium is undesirable, its omission, provided the nickel, silicon. or silicon and aluminum, are included in the proportions specified, still produces .a-steelthat-has a higher resistance to corrosion,

where salt is present in the oil, than known coma mercial steels containing a relatively hgh percentage of chro um.

My invention does not depend for its novelty upon'tiie'novelty of the composition per se,,my discoverybeingthe adaptability of th composition, not to corrosion generally, but toth'e .corrosionjof tube stills in which hydrocarbon .oil, containing salt and sulIur, is subjected to thehigh sulfur and salt are subjected to high temperature to' effect their conversion or decomposition, which comprises a tubular, container for such oils-of-an alloysteel containing carbon less than .25 mamganese in aproportion common in carbon steel, chromium .2. to less than 2%, nickel .8 to 3.5%, molybdenum..2 to 2%, a constituent of the group consisting of silicon and silicon plus aluminum .7 to 2.5%, and iron approximately suflicient to completethe the percentage of nickel bein substantially in excess of the percentage of chromium and the percentage of said silicon-containing constituent being also substantially in excess of the percentage of chromium and not less than half the percentage of nickel. V 2. A still vfor use in a process wherein hydrocarbon oils containing impurities including both sulfur and salt are subjected to high temperature to effect their conversion ordecomposition, which comprises a tubular container for such oils of an alloy steel containing carbon less than .25 manganese in a proportion common in carbon steel, chromium .2 to less than 2%, nickel .8 to 3.5%, silicon .6 to 2.4%, aluminum .1 to 1.5%, molybdenum .in' a proportion, varying approximately directly with the percentage of aluminum, within the range .4 to 2%, and iron approximately sufiicient to complete the 100%; the percentage of nickel being substantially in excess of the percentage-ofchromium and the percentage of silicon plus aluminum also substantially exceeding the percentage of chromium and beingv not'less than half the percentage of nickel. a I

AARON 7B. BAGsriR. 

